Designated Initializer Array in C

Question

I'm trying to initialize an struct array using designated initializer:

A[size].from = {[0 ... size - 1] = 0};
A[size].to = {[0 ... size - 1] = 0};

List.h:

typedef struct Buffer
{
    int from;
    int to;
}buffer_t;
typedef struct shared_memory
{
buffer_t A;
int size;
} share_t

Main.c

#include <stdio.h>    
#include "list.h"  
buffer_t A[];
int size;
void main(int argc, char *argv[])
{
    share->share_t *share = (share_t *)malloc(sizeof(share_t));
    long arg = strtol(argv[1], NULL, 10);
    size = arg;
    share->A[size] = {[0 ... size-1] = 0};
}

However this is the following error I'm receiving:

enter image description here

I'm using MinGW gcc and command prompt to compile this code and I'm writing this code in Visual studio.

Answer 1

Your code is an assignment expression, not an initializer. Initialization can only happen when an object is defined.

Also, arrays must be defined with a size. And there are better ways to zero-initialize an object than to attempt to use designated initializer ranges.

Here are two options:

int main(int argc, char *argv[])
{
    long size = strtol(argv[1], NULL, 10);
    buffer_t A[size];
    memset(&A, 0, sizeof A);

or

buffer_t *A;
size_t size;

int main(int argc, char *argv[])
{
    size = strtol(argv[1], NULL, 10);
    A = calloc(size, sizeof *A);  // already zero-initialized

The latter is probably better in that you can check for allocation failure and it supports large allocations.